Actually, smoking weed during a fast does not give me the munchies. It does it the opposite. It quietens the hunger (especially when it's purely psychological) and rejuvenates my mind, bringing motivation and self-disciple to continue the fast. Not only this, but it also helps ease away the debilitating heartburn and stomach acid, along with leaving me feeling more energetic so I can do things without being a prisoner to the weakness of a long water fast.
I don't use weed recreationally. You only get "stoned" if you smoke excessively in one sitting. I do only a hit or two for the relieving effects and renewed drive to succeed at my fast. It is a natural herb found in nature that is not really modified in any way from its original state (like cocaine or opiates). And it has the bonus of not having to go through your digestive system in order for it to work.
It's basically just using a natural remedy found in nature to assist with the miracle of nature's fasting process.
Some people drink teas, take vitamins, or even sip on some juice when points of their fast become unbearable. I take a couple of hits instead since it doesn't require waking of the stomach and digestive system. Because of this, I am able to do my fast on strictly water.
"Now that I've gotten over my initial shock of the question I'd like to point out as I'm sure you well know, one of the side effects of smoking weed is you get the munchies really bad. It seems to me if only for that reason it would be counter productive to smoke it during a fast when the main rule of the fast is not eating anything."